It's an interesting time for fans of science-fiction out there. While many of the biggest movies in the genre have tinges of sci-fi, they're mostly action-adventures in disguise, with fantastic CGI embellishments. But we've also had a string of lower-budget fare in the last few years that have embraced the more idea-led aspects of the genre -- think Duncan Jones' "Moon," Gareth Edwards' "Monsters," or Neill Blomkamp's "District 9." And the latest to join them is a man who's already made something of a specialty out of deconstructing genre tropes with his teen-noir "Brick" and meta-caper "The Brothers Bloom" -- director Rian Johnson.

It's an interesting time for fans of science-fiction out there. While many of the biggest movies purportedly in the genre have tinges of sci-fi, they're mostly action-adventures in disguise, with fantastic CGI embellishments. But we've also had a string of lower-budget films in the last few years that have embraced the more idea-led aspects of the genre -- think Duncan Jones' "Moon," Gareth Edwards' "Monsters," or Neill Blomkamp's "District 9." And the latest director to join them is a man who's already made something of a specialty out of deconstructing genre tropes with his teen-noir "Brick" and meta-caper "The Brothers Bloom" -- director Rian Johnson.

Although to hear him tell it, reinventing sci-fi wasn't his primary intention with "Looper," his imminent new film which impressed at Comic-Con over the weekend, and stars Joseph Gordon-Levitt, Bruce Willis and Emily Blunt. We spoke to Johnson on Friday, and he told us that the film "wasn't so much about coming at it wanting to tweak the genre, it was just this basic idea I'd had, of the old man and a young man; Joe working for the mob in the future, and them sending them back his older self to be killed. I'd had that very basic plot idea like ten years ago, and wrote it down as a short film that I never ended up shooting, it just sat in a drawer for ten years. And over the past couple of years, some bigger ideas attached themselves to that, and I realized 'oh this little cool plot device can make a movie that's about this.' It was nothing as conceptual as trying to do something with the genre. But having said that, I love sci-fi . When i wrote the short, I was in the middle of reading Philip K Dick's books, and I'd wanted to do something in that world for a while."

Of course, time-travel films are notoriously tricky to plot, and Johnson made a particular effort to keep things as simple as possible. "One of my big priorities in writing the script," the director said, "was to make sure that it didn't feel dense, it didn't feel like homework. I put a lot of shoe leather into going over the script, and making sure the story worked, and ticked, without the sci-fi elements complicating it too much. Making sure the time travel did its job and got out of the way. So hopefully at the end of it, it makes sense, you don't have to think about it too deeply."

Helping with advice and notes in the early stages was Shane Carruth, the man behind indie time-travel gem "Primer," a friend of Johnson. Despite some reports, however, Carruth didn't actively work on the film, although it was mooted at one point: "I was a huge fan of 'Primer,' and I met Shane just randomly through another friend, and we'd been friends for a few years. But really, Shane's only involvement was showing him the script, and getting some really good feedback from him. We talked about him doing the effects for a specific sequence in the film, and it never ended up happening, for a number of reasons. None of them bad, which is for the best, because the sequence got cut from the film anyway. So he ended up not having any direct involvement in the film."

One of the film's biggest challenges was finding a pair of actors who could plausibly play the younger and older versions of the same character, and Johnson says that, due to the older star's iconic nature, he felt that it was up to Joseph Gordon-Levitt to match his older counterpart, rather than the other way around. "If I'd put it to Bruce that we wanted to transform him," Johnson said, "I know he would have been into it, he was really gung-ho about the part, no ego at all, he was ready and up for anything. But I felt people know Bruce Willis really well, so if you try and transform him, they're gonna see right through it."